The present invention relates to apparatus for controlling gas delivery to a patient. The apparatus may provide a diagnostic and/or a therapeutic function. The diagnostic function may include monitoring and/or diagnosis of physiological variables associated with the patient. The therapeutic function may include application of controlled gas delivery to the patient.
The apparatus of the present invention is particularly useful for investigation, diagnosis and treatment of sleep, respiratory and sleep related respiratory disorders, sleep propensity and fatigue and will be described herein in that context. Nevertheless it is to be appreciated that it is not thereby limited to such applications.
Sleep apnea syndrome is a respiratory disorder affecting between 4 and 5% of the population and is now well documented in a number of reputable medical journals. Sufferers of this debilitating disorder suffer reduced sleep efficiency, excessive blood pressure, cardiovascular effect ranging from mild to fatal, amongst other adverse health consequences and risks. It is recognised that an increase in upper airway resistance attributed to relaxation of upper airway muscles during sleep, contributes to cessation of breathing at frequent intervals during an Obstructive Sleep Apnea (OSA) patient""s sleep. OSA is now relatively well documented and understood within the respiratory and sleep medical fields.
In the early 1980""s a development commonly referred to as Continuous Positive Air Pressure (CPAP) was discovered as a front line cure for OSA (Sullivan). CPAP is a device which applies a continuous positive air pressure to the patient""s airway by way of a nasal mask. This nasal mask is worn by the patient during sleep and a positive air pressure is applied to the patient""s airway in order to keep the patients airway open and prevent a collapse of the patient""s airway, which would otherwise lead to OSA.
Development of CPAP devices have been pursued by a range of manufacturers across the world and a number of variations of CPAP have also been introduced to the market place. These variations include, inter alia:
Demand Positive Air Pressure (DPAP) which is a device that supplies positive air pressure by detecting the patients respiratory cycle and applies the air pressure when the patient xe2x80x98demandsxe2x80x99 this:
Bi positive air pressure (BIPAP), which is a device that allows two states of positive pressure and monitors the patient""s respiration and delivers air pressure depending on whether the patient is undergoing inspiration or expiration; and
Variable Positive Air Pressure (VPAP) which is a device that delivers a varying air pressure depending upon the patient""s respiration cycle.
Other devices have been developed to automatically adjust air pressure delivered to a patient during sleep.
Whilst the prior art recognizes that respiratory disorders such as apnea or hypopnea may be addressed by applying positive air pressure to a patient, it has failed to recognize that even without the presence of respiratory events such as hypopnea or apnea (as detected or diagnosed by conventional means) upper airway resistance can exist and results in a reduction of a patient""s sleep efficiency. The apparatus of the present invention may diagnose such upper airway resistance by detecting arousals. Arousals may be detected, for example, from a shift in frequency of the patients Electroencephalogram (EEG) and/or Electro-oculogram (EOG).
It is therefore recognised that even after treatment for OSA by application of the above mentioned CPAP or variations thereof, a patient can still experience arousals or micro-arousals during a night""s sleep. These arousals and micro-arousals can be due in part to the fact that the air pressure required to be delivered to the patient to prevent OSA can vary depending upon the patients sleep position, sleep state and other factors such as intake of alcohol or drugs consumed prior to sleeping. The arousals and micro-arousals may be linked or associated with respiratory disorders.
It has been shown that many arousals or micro-arousals can occur during a patient""s sleep. The present invention may provide apparatus for monitoring the patient""s physiological variables and to diagnose corresponding physiological states including sleep, arousal and respiration events while at the same time controlling delivery of gas to a patient via a nasal or nasal and oral mask. The apparatus can in one mode be adapted to diagnose physiological states and in another mode adjust the pressure of air delivery to the patient to a level which accurately reflects the patient""s state of wakefulness, sleep or arousal.
Due to the complex and varying states of sleep and broad range of sleep disorders that can be diagnosed, many different physiological variables (raw data) and events (derived data) may be monitored and/or analysed. While some positive air pressure devices exist which can monitor respiratory parameters, the present applicant is not aware of any prior art device which is able to monitor and diagnose a comprehensive range of both sleep and respiratory parameters. The monitored variables/events can include one or more of the following:
Status of lights
Graphic processing of video image (allows determination of whether patients eyes are open or closed)
Patient digital video recording and graphic processing techniques for determination of eye lid activity (ie status of patient eyes being opened or closedxe2x80x94relative to fully closed or fully opened eyes status).
Time and date stamping of monitored physiological data, video and sound.
Infrared Video monitoring (for night studies)
Complex sound analysis (accurate full bandwidth or limited bandwidth recording and analysis of breathing sounds).
Physiological events: ie ECG arrhythmia, EEG spike detection, EEG spindles amongst others
Endoscopy
Breath by breath analysis-pnuemotachograph
3D imaging
Infrared eye detection for fatigue and sleep monitoring
EEG delta and alpha-wave detection
Delta Wave detections and related sleep/fatigue/impairment detection
Mattress Device: monitoring of patient sleep state and respiratory parameters by using a mattress sensor device. The matress device can be used to monitor a patient""s electro-oculogram, sleep state, arousals, position, electrocardiogram. There are presently two types commercially available mattress devices; Static Charge-sensitive Bed (SCSB) and polyvinylidene fluoride (PVDF-piezoelectric plastic).
The apparatus of the present invention may monitor and diagnose a patient""s EEG, EMG, EOG, position, breathing/snoring sounds and other variables/events while; at the same time control treatment such as positive air pressure. The positive air pressure treatment may be adjusted dynamically to suit the patients prevailing:
sleep state, respiratory events (ie OSA, central apnea, hypopnea, mixed apnea)
position (different air pressure may be required depending upon the patient""s sleep position),
arousals status (ie micro arousals may occur due to insufficient or excessive pressure),
snoring (varying degrees of pressure may be required depending upon the patient""s snoringxe2x80x94if for example the patient has taken alcohol or other drugs prior to their sleep, CPAP pressure may need to be varied in order to effectively eliminate snoring).
The apparatus of the present invention may deliver small or large adjustments in gas pressure delivery to the patient in order to maintain an appropriate pressure at all times.
The apparatus of the present invention may operate in one of several modes. The apparatus may operate in a diagnostic mode in which patient variables and/or events are monitored, processed and recorded for later review. Processing of the variables/events may be performed in any suitable manner and by any suitable means such as by means of a system as disclosed in AU Patent 632932 entitled xe2x80x9cAnalysis system for physiological variablesxe2x80x9d. The diagnostic mode may include means for determining patient states. The latter may be derived from the monitored variables/events by means of one or more known automated sleep staging methodologies. The diagnostic mode includes means for determining an appropriate gas pressure setting for each patient state. The latter may be carried out by means of a pressure setting algorithm and stored in a look-up table for recall during the treatment mode.
The apparatus may operate in a treatment only mode wherein pressure settings determined during the diagnostic mode and stored in the look-up table may be applied to deliver gas to a patient according to the prevailing state of the patient as determined during the treatment mode.
The apparatus may operate in an integrated diagnostic and treatment mode wherein treatment via gas delivery is related to the currently monitored patient variables/events and diagnosed physiological states of the patient. The latter are determined in real time as part of the diagnostic mode.
A significant function of the diagnostic and integrated modes is to monitor the patient for micro-arousals. These micro-arousals can be detected from a change in frequency of the EEG and/or the EMG channels and/or by other means such as by detecting patient position/movement or by monitoring a mattress sensor device. By detecting the patient""s micro-arousals, treatment of gas delivery can be correctly verified as providing an appropriate gas delivery for the patient. This method of arousal monitoring may determine whether or not the patient is actually being treated and benefiting from optimal sleep efficiency during gas delivery treatment.
The apparatus, includes means for monitoring one or more physiological variables including EEG, EOG, EMG, patient position and breathing/snoring. The monitoring means may include one or more transducers adapted to monitor the relevant physiological variable(s) such as a microphone for monitoring breathing/snoring sounds, and to provide an analog signal output indicative of the monitored variable. The monitoring means may include one or more electrodes applied to a part or parts of the body of the patient such as the skull, canthus, chin, legs etc. The monitoring means may also include means suitable for monitoring inter alia, oxygen saturation, CO2 levels, respiratory effort, breathing and snoring sounds.
The apparatus includes means for analog processing the or each channel or signal obtained by the monitoring means. The analog processing means may include means for preamplifying conditioning and filtering the signal(s). The apparatus may include means for converting the processed signal(s) to a digital signal(s). The conversion may be carried out in any suitable manner and by any suitable means such as an analog to digital converter.
The apparatus includes means for processing the digital signal(s). The digital processing means may include a digital computer such a microprocessor or microcomputer. The digital processing means may be programmed via suitable software means to derive from the monitored physiological variables corresponding patient states and/or events. The processing means may make use of one or more algorithms to automatically derive the patient states and/or events.
The algorithm(s) may be adapted to derive, inter alia, hypopnea, obstructive apnea, central apnea and mixed apnea respiratory events, arterial oxygen desaturation (SaO2), wake, arousal and REM sleep states, and stages 1, 2, 3 or 4 of sleep for each epoch. The number of epochs entered for each state may vary but should be sufficient to allow a measure of confidence for each patient state. For example, if there were only one epoch of REM sleep considered stable, this may prompt a clinician to review the patient""s data as there may be a case for further investigation due to a below normal occurrence of REM sleep. A sequence of patient states for each epoch may be derived via this process. Where a large range and types of variables are being monitored, the processing means may be adapted to limit the number of patient states, or combination of states which may be recognised in order to simplify configuration options and system use. The states/combinations available may depend upon the end use of the apparatus eg. whether the apparatus is intended to be used as a routine clinical tool or a research device.
The apparatus may include means for determining an appropriate gas delivery pressure for each patient state and/or context of patient states or combinations thereof. The context may refer to a current combination of states or preceding states or combinations thereof. The pressure determining means may include means for increasing pressure in the event that a deterioration in respiratory event such as snoring, SaO2 desaturation, obstructive apnea, mixed apnea, central apnea, hypopnea or the like is detected. The pressure may continue to be increased until the event ceases, subject to a recommended maximum pressure not being exceeded. To more accurately establish a target pressure value wherein an increase in gas pressure ceases to cause improvement in effective breathing, it may be desirable to slightly overshoot the target value. Pressure may then be reduced upon detecting that a monitored event has deteriorated. The apparatus may also include means for detecting central apnea events triggered by the brain. In central apnea events gas delivery pressure changes may have little or no effect on a patient""s respiratory function. It is therefore desirable to establish a central apnea condition before responding excessively to a respiratory event.
In one form the digital processing means may be programmed via suitable software to determine from each patient state and/or their contexts a gas pressure value beyond and below which there is a deterioration in a monitored event. The means for determining the appropriate gas delivery pressure may include a pressure seek algorithm. The algorithm may ensure that pressure to a patient is tracked up or down until it is appropriate for a prevailing event such as a stage of sleep. The algorithm may also ensure that the state of the patient is stable before recording a pressure value for the prevailing epoch. A table of pressure values for each patient state may be derived by this process. The table may indicate the number of epochs associated with a particular pressure value or values. It is expected that readings over several epochs will cluster around a narrow range of pressure values for each patient state.
The table may be stored in a memory associated with the processing means. The memory, may be on board the apparatus or it may be located remotely from the apparatus and connectable thereto via any suitable means such as a telecommunication line and modern. In one form the remote memory may include a portable carrier such as a magnetic or smart card.
A process of seeking an appropriate gas delivery pressure values may be commenced with a default or manually entered value for each patient state. Values may be entered manually by a physician either locally or remotely. Default values may be determined from clinical trials. The default and manually entered values may be entered in a table of default pressure values.
Where the apparatus is to be operated in an integrated diagnostic and treatment mode, pressure values which are determined by the pressure seek algorithm may be used to control in real time a gas delivery device via a suitable interface. The gas delivery device may comprise a CPAP device or other externally controllable gas or air flow delivery unit. The pressure values which are determined by the pressure seek algorithm may be entered in a pressure set look-up table and retained for future use.
Where the apparatus is to be operated in a treatment mode, the pressure values which are stored in the pressure set look-up table may be accessed following patient state determination. The values entered in the pressure set look-up table may be used to control directly a gas delivery device. During treatment mode, pressure values appropriate to each patient state determined during the integrated diagnostic mode may be used. This may enable direct treatment of a patient where pressure values appropriate to each patient state have previously been determined for that patient.
Where the apparatus is to be operated in a diagnostic mode, data representing patient states derived from the monitored physiological variables may be recorded for later recall and review.
According to one aspect of the present invention there is provided apparatus for controlling gas delivery to a patient, said delivery being adapted to maintain a physiological event such as effective respiratory function and/or absence of arousals, said apparatus including:
means for monitoring one or more physiological variables associated with said patient;
means for deriving from said one or more variables, data representing physiological states of said patient corresponding to the or each variable; and
means for determining from said data for each physiological state, a gas pressure value beyond and below which there is a deterioration in said event.
According to a further aspect of the present invention there is provided a method for controlling gas delivery to a patient, said delivery being adapted to maintain a physiological event such as effective respiratory function and/or absence of arousals, said method including the steps of:
monitoring one or more physiological variables associated with said patient;
deriving from said one or more variables, data representing physiological states of said patient corresponding to the or each variable; and
determining from said data for each physiological state, a gas pressure value beyond and below which there is a deterioration in said event.